Process for obtaining high conductivity copper alloys

ABSTRACT

AN IMPROVED PROCESS FOR OBTAINING HIGH CONDUCTIVITY COPPER BASE ALLOYS IN WHICH THE ALLOY IS HEATED AT 700 TO 1000*C. FOR AT LEAST 30 MINUTES, HOT ROLLED, COOLED TO BELOW 300*C. AT A RATE OF GREATER THAN 550*C./HOUR, COLD ROLLED BELOW 200*C. AND THEN AGED AT 250 TO 575* C. FOR AT LEAST ONE HOUR.

United States Patent U.S. Cl. 14812.7 9 Claims ABSTRACT OF THE DISCLOSURE An improved process for obtaining high conductivity copper base alloys in which the alloy is heated at 700 to 1000 C. for at least 30 minutes, hot rolled, cooled to below 300 C. at a rate of greater than 550 C./hour, cold rolled below 200 C. and then aged at 250 to 575 C. for at least one hour.

This application is a continution-in-part of US. patent application Ser. No. 581,713, filed Sept. 26', 1966, for Process for Obtaining 'High Conductivity Copper Alloys, by 'Elmars Ence, now abandoned.

It is, course, highly desirable to obtain high conductivity copper alloys having good strength characteristics. However, alloys of this type are either not readily available or quite expensive.

In copper base alloys a common method for obtaining good strength characteristics is by alloying. Alloying, however, normally lowers the conductivity, for example, solid solution hardening depends upon keeping alloying additions in solution. This is mutually incompatible with high conductivity.

There are other strengthening phenomena, such as precipitation hardening, dispersion hardening, order-disorder reactions, and martensite reactions. These also require the presence of alloying additions which in general are not completely removed from th copper matrix and, therefore, detract from the conductivity of the alloy.

Accordingly, it is a principal object of the present invention to provide a process for obtaining high conductivity copper base alloys.

It is a further object of the present invention to provide a process for obtaining high conductivity copper base alloys having good strength characteristics.

It is a still further object of the present invention to provide a process as aforesaid which obtains alloys at a reasonable cost.

Further objects and advantages of the present invention will appear hereinafter.

In accordance with the present invention, it has now been found that the foregoing objects and advantages may be readily obtained. The process of the present invention comprises:

(A) providing a copper base alloy selected from the group consisting of (1) from 0.1 to 2.5% chromium, 0.01 to 0.5% phosphorus, preferably 0.001 to 0.25% boron and the balance essentially copper,

(2) from 0.5 to 4.0% iron, from 0.2 to 2.5% cobalt, and either phosphorus from 0.01 to 0.5% or boron from 0.001 to 0.25% or both phosphorus and boron in the foregoing amounts, balance essentially copper,

(B) heating said alloy at a temperature of from 700 to 1000 C. for at least 30 minutes and hot rolling said alloy in the foregoing temperature range;

(C) cooling said alloy to below 300 C. at a rate greater than 550 C. per hour; and

3,573,110 Patented Mar. 30, 1971 (.D) heating said alloy at a temperature of from 250 to 575 C. for at least one hour.

In accordance with the present invention it has been found that the foregoing process yields alloys retaining high conductivity While having improved strength characteristics. For example, the conductivity of the foregoing alloys are in excess of IACS and generally in excess of IACS while the yield strengths are in excess of 40,000 p.s.i. and generally in excess of 50,000 p.s.i.

The fore-going improvements are attained in part due to the specific alloying additions and in part due to a method of treatment which precipitates secondary hard ening phases of the alloying additions and disperses them throughout the copper matrix, resulting in improved strength while retaining high conductivity. The secondary hardem'ng phases may be in either elemental form or intermetallic compound form. That is, the alloying additions in the foregoing amounts can be essentially precipitated from solid solution so that the copper matrix attains high conductivity but at the same time develops good strength through processing to disperse the hardening phases throughout the copper matrix.

In accordance with the process of the present invention two types of copper base alloys may be utilized. One type contains from 0.5 to 4% iron and preferably from 1.1 to 2.0%, and from 0.2 to 2.5% cobalt and preferably from 0.3 to 1.0%. In addition, these alloys contain either phosphorus or boron or both in the following amounts: phosphorus from 0.01 to 0.5% and preferably from 0.05 to 0.15%; and boron from 0.001 to 0.25% and preferably from 0.005 to 0.05%. In addition, cerium may be added in an amount from 0.2 to 2.0% and preferably from 0.3 to 1.0%.

The other type of alloy contains from 0.1 to 2.5% chromium and preferably from 0.75 to 1.25% chromium. Phosphorus is present in an amount from 0.01 to 0.5% and preferably from 0.05 to 0.15%. It is preferred to use boron in an amount from 0.0011 to 0.25 and preferably from 0.005 to 0.05%. All percentages of ingredients are percentages by weight.

While excessive amounts of impurities are to be avoided, small amounts of impurities or other alloying additions may, of course, be tolerated provided that they do not greatly reduce the strength or conductivity characteristics. Also, naturally, alloying additions may be utilized in order to achieve a particular result.

In accordance with the present invention the melting and casting of the copper base alloys of the present invention are not particularly critical, although in the higher iron and cobalt ranges, higher melting and casting temperatures may be necessary. The alloys may be melt and cast in accordance with conventional techniques for these copper base alloys, e.g., the alloys may be prepared using conventional induction melting techniques with the alloying additions preferably made in the form of copper master alloys. For example, in order to provide reasonable melting temperatures, it may be advisable to use a 5 to 10% cobalt master alloy, a 5 to 10% iron master alloy, a 5 to 10% chromium master alloy, a 1% boron master alloy, and a 10 to 15% phosphorus master alloy.

After casting the ingots are heated for hot rolling to a temperature of between 700 and 1000 C. and preferably 850 to 975 C. A holding time at this temperature of at least 30 minutes is preferred. The ingots are then hot rolled in the above temperature range to convenient gage. This hot rolling could, if desired, be the final rolling step. The amount of reduction in the hot rolling step is not particularly critical. If desired, the ingots may be hot rolled above 500 C. and preferably from 850 to 975 C., cooled at any desired cooling rate, and solution heat treated as above, i.e., 700 to 1000 C., preferably 850 3 to 975 C. for at least 30 minutes. In other words, the order of hot rolling and heat treating may be reversed.

After heat treating and hot rolling, or after hot rolling and heat treating, the strip must be rapidly cooled to below 300 C. at a rate of not less than 550 C. perhour and preferably at least 550 C. per minute. This is necessary to maintain alloying additions in solid solution so that they may be substantially precipitated in a proper dispersion to attain the desired strength and conductivity.

The alloy may, if desired, be cold rolled after rapid cooling. The cold rolling step is optional and depends upon gage requirements. The cold reduction step may attain a reduction up to 96% in one or more passes. The temperature of the cold reduction is not particularly critical but is generally below 200 C.

Whether or not the material is to be cold rolled, it must ultimately receive a thermal aging treatment which serves to precipitate constituents from solid solution and achieve the desired properties. This aging treatment may also serve as an interanneal or final anneal when cold rolling is used. This aging treatment should be at 250 to 575 C. for at least 1 hour and preferably less than 50 hours.

If desired, the strip may be interannealed once or more between cold rolling passes. Strip annealing techniques may be used, in which case the holding times are usually short, i.e., from 15 seconds to minutes, and possibly as long as one hour, and the temperature is from 250 to 600 C. Batch annealing techniques may also be used in which case temperatures of 250 to 575 C. for up to 24 hours may be used. If interanneals are employed, the total time at temperature should preferably be less than about 30 hours in order to achieve preferred properties. Cooling rates from this temperature range are not critical.

As stated hereinabove, some time during the processing an aging treatment must be employed. This may be after the final cold rolling pass, if the alloy is cold rolled, or after the rapid cooling step if no cold reduction is utilized. The aging treatment may also precede a final cold reduction. This is a critical step of the present invention. The temperature of the critical anneal or aging treatment is from 250 to 575 C. and the holding times are at least one hour and generally less than 50 hours. The particular temperature and holding time chosen will depend upon the combination of strength and conductivity required. Normally, the aging treatment is conducted in a bell type furnace which has a controlled atmosphere, however, this is not essential.

If desired, the following modification in the foregoing procedure may be employed. After the rapid cooling step the alloy may be cold rolled, for example, at a reduction between 30 and 70%, at a temperature of below 200 C. This may be followed by the critical aging step of the present invention, i.e., at 250 to 575 C. for at least one hour. The alloy may then be cold rolled below 200 C., with reduction depending on gage requirements followed by strip or batch annealing, as indicated hereinabove. As many cycles of cold rolling and strip or batch annealing may be used to reach desired gage. Optionally, this may be followed by another critical anneal or aging treatment, if desired.

The resultant alloy attains the aforementioned desirable combination of strength and conductivity. The alloying additions are precipitated in a substantially fine, uniform dispersion throughout the copper matrix.

The present invention will be more readily apparent from a consideration of the following illustrative examples.

EXAMPLE I An alloy of the present invention was prepared by conventional techniques used for preparation of alloys of the type including an induction furnace, a sutiable crucible material, and protection of the molten metal from oxygen by an inert or reducing atmosphere.

OFHC-grade copper was melted down and the temperature of the melt raised to about 1200 to 1250 C. Chromium was added as a copper-5 to 10% chromium master alloy. After the copper-chromium master had completely dissolved, phosphorus and boron were added to the melt in the form of a copper-1O to 15% phosphorus master alloy and copper-1% boron master alloy. The melt was then held at temperature for about 5 to 10 minutes during which time the melt was stirred and cast into cast iron molds. The composition of the resultant alloy was 0.9% chromium, 0.1% phosphorus, 0.02% boron and the balance essentially copper.

EXAMPLE II The ingot prepared in Example I was hot rolled at 950 C. to 0.5 thickness and subsequently solution heat treated for one hour at 925 C. followed by Water quenching to room temperature in 5 seconds. The resultant alloy was cold rolled to 0.025 gage.

High strength and high electrical conductivity was developed in two samples by final heat treatments of four and 24 hours at temperatures of 400 to 500 C. The properties of these materials are shown in Table I below with Alloy 1 being heat treated for four hours, and Alloy 2 being heat treated for 24 hours. Also shown in Table I below for comparison are properties of a copper-0.9% chromium alloy identified as Alloy 3 in the table below.

TABLE I Alloy 1 Alloy 2 Alloy 3 Yield strength, 0.2% ofiset, p.s.i 70,150 69, 800 45, 000 Ultimate tensile strength, p.s.i 74, 300 74, 000 50, 000 Elongation, percent 11 13 15 Electrical conductivity, percent IACS.. 81 86 81 The microstructures of Alloys 1 and 2 were characterized as follows: The alloying additions were precipitated in a fine, uniform dispersion throughout the copper matrix EXAMPLE III EXAMPLE IV An alloy of the present invention was prepared by conventional techniques used for preparation of alloys of this type including an induction furnace, a suitable crucible material, and protection of the molten metal from oxygen by an inert or reducing atmosphere.

OFHC-grade copper was melted down and the temperature of the melt raised to about 1200 to 1250 C. Iron and cobalt were added as a copper-5 to 10% cobalt master alloy and copper-5 to 10% iron master alloy. After the alloying additions had completely dissolved, phosphorus and boron were added to the melt in the form of a copper-10 to 15% phosphorus master alloy and copper-1% boron master alloy. The melt was then held at temperature for about 5 to 10 minutes during which time the melt was stirred and cast into cast iron molds. The composition of the resultant alloy 1.5% cobalt, 2.5% iron, 0.03% phosphorus, 0.02% boron and the balance essentially copper.

EXAMPLE V The ingot prepared in Example IV was hot rolled at 950 C. to 0.5 thickness and subsequently solution heat treated for one hour at 925 C. followed by water quenching to room temperature in 5 seconds. The resultant alloy was cold rolled to 0.025" gage.

High strength and high electrical conductivity was developed by a final heat treatment of 24 hours at 500 C. The properties of this material is shown in Table II below identified as Alloy 5. Also shown in Table II below for comparison are properties of a copper-0.9% chromium alloy identified as Alloy 6 in the table below.

TABLE II Alloy Alloy 6 Yield strength, 0.2% offset, p 53, 600 45, 000 Ultimate tensile strength, p. 67, 800 50, 000 Elongation, percent. 15 15 Electrical conductivity, percent mos .1 s1 31 The microstructure of Alloy 5 was characterized as follows: The alloying additions were precipitated in a fine, uniform dispersion throughout the copper matrix.

EXAMPLE VI EXAMPLE VII After the treatment of Example VI, Alloy 7 was cold rolled 50% and heat treated for 24 hours at 400 C. The properties were: yield strength at 0.2% offset-41,700 p.s.i.; ultimate tensile strength-60,700 p.s.i.; elongation- 17%; and conductivity82.5% IACS.

EXAMPLE VI-II Alloy compositions identified as Alloys 8, 9, 10 and 11 were prepared by melting in an induction furnace under a charcoal cover. The copper was added as OPEC copper, the iron was added in the form of low carbon 1010 steel, the cobalt as powder metal briquettes, the phosphorus as a Cu-14% phosphorus master alloy, and the boron as a Cu-1% boron master alloy. The melt was held at 1300 C. for 15 minutes prior to casting into a cast iron mold. These alloys were hot rolled at 925 C., reducing the thickness from 1.25 down to 0.4". They were air cooled to room temperature and then reheated for solution heat treating to 925 C. for one hour, followed by water quenching. They were then cold rolled to a 94% reduction in thickness and finally given an aging-annealing treatment at 480 C. for 24 hours. The composition of Alloys 8, 9, 10 and 11 are shown in Table III and the properties obtained are shown in Table IV.

This invention may be embodied in other forms or carried out in other ways without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered as in all respects illustrative and not restrictive, the scope of the invention being indicated by the appended claims, and all changes which come within the meaning and range of equivalency are intended to be embraced therein.

What is claimed is:

1. A process for providing high conductivity, high strength copper base alloys which comprises:

(A) providing a copper base alloy selected from the group consisting of (1) an alloy containing as alloying additions from 0.1 to 2.5% chromium, from 0.01 to 0.5% phosphorus and the balance essentially copper, and

(2) an alloy containing as alloying additions from 0.5 to 4.0% iron, from 0.2 to 2.5% cobalt, a material selected from the group consisting of from 0.01 to 0.5% phosphorus, from 0.001 to 0.25% boron and mixtures thereof, and the balance essentially copper;

(B) heating said alloy at a temperature of from 700 to 1000 C. for at least 30 minutes and hot rolling said alloy in the foregoing temperature range;

(C) cooling said alloy to below 300 C. at a rate greater than 550 C. per hour and. cold rolling said alloy below 200 C.; and

(D) heating said alloy at a temperature of from 250 to 575 C. for at least one hour,

thereby precipitating the alloying additions throughout the copper matrix in a substantially fine, uniform dispersion.

2. A process according to claim 1 wherein said alloy is (A) (1) and contains from 0.001 to 0.25% boron.

3. A process according to claim 1 wherein said alloy is (A) (2) and contains iron, cobalt, phosphorus and boron.

4. A process according to claim 1 wherein in step (B) the alloy is first hot rolled above 500 C. followed by holding at a temperature of from 700 to 1000 C. for at least 30 minutes.

5. A process according to claim 1 wherein in step (C) said alloy is cooled at a rate greater than 550 C. per minute.

6. A process according to claim 1 wherein said alloy is cold rolled a plurality of times with interannealing between cold rolling passes.

7. A process according to claim 1 wherein in step (D) the alloy is heated for from 1 to 50 hours.

8. A process according to claim 1 wherein after step (D) the alloy is cold rolled at below 200 C. followed by annealing.

9. A process according to claim 8 wherein after said annealing the alloy is heated at a temperature of from 250 to 575 C. for at least one hour.

References Cited UNITED STATES PATENTS 1,723,867 8/1929 Korsunky -153 2,123,629 7/1938 Hensel et al. 75153 2,147,844 2/1939 Kelly 75--153 2,281,691 5/1942 Hensel et al 148--12.7 3,039,867 6/1962 McClain 75153 L. DEWAYNE RUTLEDGE, Primary Examiner W. W. STALLARD, Assistant Examiner 

